1. Field of the Invention
The present invention relates to an electrically erasable and programmable read only memory (EEPROM) device and a method of manufacturing an EEPROM device. More particularly, the present invention relates to an EEPROM device having a relatively simple structure capable of achieving a relatively large integration degree and a reliability and a method of manufacturing the EEPROM device capable of reducing cost and time required to manufacture the EEPROM.
2. Description of the Related Art
Generally, a semiconductor memory device may be classified as a volatile semiconductor memory device or a non-volatile semiconductor memory device. The volatile semiconductor memory device may be a dynamic random access memory (DRAM) device or a static random access memory (SRAM) device. The volatile semiconductor memory device might not retain its data when a time elapses. However, it may take less time to input or output data in the volatile memory device. The non-volatile semiconductor memory device may retain its data even when a time elapses. However, it may take greater time to input or output data in the non-volatile memory device. Recently, the non-volatile semiconductor memory device such as an electrically erasable and programmable read only memory (EEPROM) device and a flash memory device is much in demand.
A memory cell of a conventional EEPROM device may include a memory transistor and a selection transistor. For example, a conventional EEPROM device is disclosed in Korean Patent No. 341657 and Korean Patent Laid-Open Publication No. 2006-32868.
FIGS. 1 to 7 are cross-sectional views illustrating a method of manufacturing the conventional EEPROM device disclosed in Korean Patent Laid-Open Publication No. 2006-32868.
Referring to FIG. 1, an isolation layer (not shown) is formed at a surface of a substrate 3 so that the substrate 3 may be divided into a memory transistor region I and a selection transistor region II.
Tunnel impurity regions 6 are formed at a surface portion of the substrate 3 located between the memory transistor region I and the selection transistor region II. Thereafter, a first mold layer 9, a second mold layer 12, and a third mold layer 15 may be subsequently formed on the substrate 3, where the tunnel impurity regions 6 are formed. The first, second, and third mold layers 9, 12 and 15 may be formed using a silicon oxide, a silicon nitride, and a silicon oxynitride, respectively.
Referring to FIG. 2, a first mold layer pattern 18, a second mold layer pattern 21, and a third mold layer pattern 24 are subsequently formed on the substrate 3 by patterning the first, second, and third mold layers 9, 12 and 15.
The memory transistor region I may be exposed when the first, second, and third mold layer patterns 18, 21 and 24 are formed. This is because the first, second, and third mold layer patterns 18, 21 and 24 are formed on the selection transistor region II.
A tunnel insulating layer 27 is formed on the substrate 3 to cover the third mold layer pattern 24. The tunnel insulating layer 27 may be formed using the silicon oxide to cover the selection transistor region II that is not covered with the first, second and third mold layer patterns 18, 21 and 24.
Referring to FIG. 3, a nitride layer is formed on the tunnel insulating layer 27. Thereafter, the nitride layer and the tunnel insulating layer 27 are partially etched until the memory transistor region I and third mold layer pattern 24 are exposed so that a tunnel insulating layer pattern 30 and a spacer 33 may be formed on sidewalls of the first, second, and third mold layer patterns 18, 21 and 24.
A gate insulating layer 36 is formed on the memory transistor region I that is not covered with the tunnel insulating layer pattern 30 and the spacer 33. The gate insulating layer 36 may include silicon oxide. The gate insulating layer 36 may have a thickness larger than that of the tunnel insulating layer pattern 30.
Referring to FIG. 4, the spacer 33 is removed from the tunnel insulating layer pattern 30. A first conductive layer is then formed on the gate insulating layer 36, the tunnel insulating layer pattern 30, and the third mold layer pattern 24. The first conductive layer may include polysilicon doped with impurities.
The first conductive layer is partially removed until the third mold layer pattern 24 is exposed so that a first conductive pattern 39 is formed on the gate insulating layer 36. The third mold layer pattern 24 is then removed from the second mold layer pattern 21. The first conductive pattern 39 may serve as a floating gate of the memory transistor.
Referring to FIG. 5, the second mold layer pattern 21 located on the first mold layer pattern 18 is removed so that the tunnel insulating layer pattern 30 formed on the sidewalls of the first conductive layer pattern 39 and the first mold layer pattern 18 may be exposed.
A sidewall spacer 42 is formed on the sidewalls of the exposed first mold layer pattern 18 and the exposed tunnel insulating layer pattern 30. The first mold layer pattern 18 located on the selection transistor region II is then removed. Accordingly, the selection transistor region II may be exposed again by removing the first mold layer pattern 18.
A gate insulating interlayer 45 is formed on a resultant area formed between the exposed selection transistor region II and the memory transistor region I. For example, the gate insulating interlayer 45 may be formed to cover the sidewall spacer 42, the tunnel insulating layer pattern 30, and the first conductive pattern 39 within the memory transitory region I.
Referring to FIG. 6, a second conductive layer 48 is formed on the gate insulating interlayer 45. The second conductive layer 48 may be formed using polysilicon or metal silicide.
The second conductive layer 48 is partially etched by a photolithography process so that a hole 51 exposing a portion of the memory transistor region I is formed. A source region 54 is formed at the exposed memory transistor region I by an ion implantation process. The source region 54 located between the tunnel impurity regions 6 may be formed within the memory transistor region I located between the tunnel impurity regions 6.
Referring to FIG. 7, a control gate 57 of a memory transistor 72 and a selection gate 60 of a selection transistor 75 are formed by patterning the second conductive layer 48. The gate insulating interlayer 45 is then patterned so that gate insulating interlayer patterns 63 may be formed. The gate insulating interlayer patterns 63 are formed between the first conductive pattern 39 serving as a floating gate and the control gate 57 within the memory transistor region I. In addition, the gate insulating interlayer patterns 63 are formed between the substrate 3 and the selection gate 60 within the selection transistor region II.
An insulating layer may be formed on the substrate 3 to cover the memory transistor 72 and the selection transistor 75. Gate spacers 66 may be then formed on sidewalls of the memory transistor 72 and the selection transistor 75 by anisotropically etching the insulating layer.
A drain region 69 located between the selection gates 75 is formed within the selection transistor region II by an ion implantation process employing the selection transistor 75 and the gate spacer 66 as ion implantation masks. Accordingly, the EEPROM device may be manufactured on the substrate 3.
However, the above EEPROM device includes the memory transistor and the selection transistor having different structures so that the number of processes required for manufacturing the EEPROM device is relatively large. Thus, cost and time required for manufacturing the EEPROM device may increase. In addition, a yield of the EEPROM device may decrease. Recently, a size of a unit memory cell included in the EEPROM becomes smaller to achieve a relatively large capacity. However, it is difficult to reduce the size of the unit memory cell included in the EEPROM device because the memory cell of the EEPROM device includes the transistors having different structures. In addition, a reliability of the EEPROM device may be inferior because relatively complex processes are required to manufacture the EEPROM device.